Sonographic appearance of syphilitic induration in the lower
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A 25-year-old Japanese woman was referred with an intractable, sclerotic lesion in her lower lip that was thought to be a malignant tumor. She had been healthy until she noticed a painless nodule in her lower lip 4 weeks ago.

She reported a history of unprotected orogenital contact with a steady male partner approximately 3 weeks before the onset of a painless tumor. A physical examination revealed that she had a nodule in her lower lip, which was approximately 2.0 cm in diameter. It had an ulcer-like lesion in the center and a slightly elevated erythematous and indurated margin.

A complete blood count (CBC) and biochemical tests were within reference ranges, except for an elevated C-reactive protein level of 6.48 mg/dL. Tests for human immunodeficiency virus (HIV) I/II antibodies, hepatitis B (HB) antigen, and hepatitis C virus (HCV) antibodies were negative; these test results were additionally confirmed to be negative 1 month later.

An ultrasonographic examination was performed to determine the invasion range of the mass. The examination was performed by a well-trained sonographer. The lesion revealed an oval-shaped tumor measuring 17 × 11 × 12 mm in size, with heterogenous internal echo and unclear border. Color Doppler sonography showed very abundant blood flow signal, except for in the center of the tumor. Pressure testing with a probe revealed that the tumor was soft, suggesting an inflammatory mass, rather than neoplastic. It was not possible to perform multiple resonance imaging (MRI) because one of her front teeth had a metal crown.

Syphilis serology tests were added following ultrasonography. A quantitative antibody test for Treponema pallidum (anti-T. pallidum antibody) was high at 115.1 U/mL. A reactive rapid plasma reagin (RPR) test was strongly positive with a titer of 2060 RU. A fluorescent treponemal antibody-absorption (FTA-ABS) test was strongly positive (1:320).

A biopsy of a small part of the sclerotic lesion was performed. A diagnosis of syphilis was made, with lower lip induration as the primary lesion. Amoxicillin (AMPC) 1500 mg was administered orally for 4 weeks. Her lip lesion had almost resolved after 3 months. She did not show antibacterial side effects. An RPR test became negative with a titer of 0.3.